1. Field of the Invention
This invention relates generally to containers, and particularly to containers such as metal cans and the metal can ends that are designed to be fastened and sealed to such containers.
2. Description of the Related Technology
Containers such as metal cans are typically filled at a packaging facility and then sealed by applying a metallic can end that is usually fastened to the can using the well-known double seaming process. The term “easy open end” is used generally for that class of ends for containers that are provided with a built-in mechanism for permitting the consumer to open the container at the end for access to the ingredients within the container, without requiring the use of a can opener or other external tool. One conventional easy open end employs a pull tab having a pointed nose, the pull tab being riveted to the panel of the end so that the nose rests adjacent a weakened area along the periphery of the end panel. To open, the pull tab is rotated in a vertical plane about the rivet, causing the nose to fracture the weakened area. Further pulling of the tab away from the end panel then causes the remainder of the weakened portion of the end panel along the score line to rupture, thereby permitting the end to be opened and the contents of the container to be accessed.
One type of easy-open end that is in wide use is the so called “full-open” end, in which a peripheral score, generally circular in configuration, is formed in the end panel at or adjacent to the periphery thereof to permit its complete removal. Full-open type cans are to be distinguished from those self opening cans which have a comparatively small removable section which, when opened, provide a comparatively small hole for dispensing the product. The latter type of can end is more appropriate for packaging soda, beer, or other liquids. Full-open type cans, on the other hand, are suitable for packaging solid products such as candy, nuts, meats, or ground coffee.
The integrity of metallic can ends must periodically be checked as a matter of quality control during the packaging process. There are a number of known systems and techniques available for such testing. One example is the Borden tester, the basic configuration of which is generally disclosed in U.S. Pat. No. 3,499,314 to Roberts et al. In that device, the can end is positioned within a testing fixture and a pressure differential is induced between the two sides of the can end. A transducer detects any seepage of gas that occurs through a defective can end and a sorting apparatus disposes of the leaky, defective can ends.
In addition, the fill level of product within the cans must periodically be checked at the packaging facility. There are also a number of known systems and techniques available for checking the fill level of sealed containers. For example, the size of the headspace within the container may be detected by placing the container within a pressurized or depressurized chamber and monitoring the flexure of the end panel of the can end. In other systems, vibration or sound may be applied to the sealed container and the response of the container or of the end panel may be measured. In such systems, it generally can be determined whether the lower portion of the end panel is in contact with the product.
While existing testing technology has been satisfactory in some respects, a need continually exists for improved packaging technology and improved systems and processes for testing can ends and monitoring the fill level of containers.